The objective of this study is to determine the role played by light induced free raidcals in chemically induced skil photosensitivity. Irradiation of the following drugs in aqueous or organic solution has been shown to produce a variety of free radicals: sulfanilamide, sulfacetamide, sulfadiazine, carbutamide, tolbutamide, benoxaprofen and musk ambrette. These photo induced free radicals may play an important role in the phototoxic and photoallergic properties of these compounds.